Colored rutile boules and method of making the same

ABSTRACT

SINGLE CRYSTAL RUTILE BOULES MODIFIED WITH BOTH TUNGSTEN AND NICKEL ARE PRODUCED WHICH VARY IN COLOR FROM YELLOW TO REDDISH AMBER. THE BOULES ARE PORDUCED BY MIXING EQUIMOLAR QUANTITIES OF NICKEL AND TUNGSTEN OXIDES .006.03% MIO AND 0.02-0.8% WO3 BY WEIGHT OF TIO2, WITH RUTILE FEED POWDER FUSING SAID MIXTURE WITH A PLASMA OF FLAME HEAT SOURCE TO FORM A SINGLE CRYSTAL BOULE. THE BOULES PRODUCED HAVE POTENTIAL UTILITY AS A GEM MATERIAL OR IN MICROWAVE MASER APPILICATIONS.

March 12, 1974 COLORED RUTILE BOULES AND METHOD OF MAKING THE SAMEABSORPT/O/V COEFF/C/ENT (/7' J. D. CHASE 3,796,584

Filed Aug. 14, 1972 ABSORPT/O/V COEFF/C/ENTS //v V/S/BLE PEG/0N FORHUT/LE A/VD RU T/LE MOD/F/ED W/TH 0x/0E5 0F TU/VGSTE/V f NICKEL\\/RUT/LE m0 W03 RUT/LE l l l I l l 5500 4000 4500 5000 5500 5000 5500WAVELENGTH (A0) INVENTOR.

JOH/V 00/vALO CHASE 7M QAEMZ D ATTORNEY United States Patent Oflice3,796,584 Patented Mar. 12, 1974 3,796,584 COLORED RUTILE BOULES ANDMETHOD OF MAKING THE SAME John Donald Chase, Stamford, Conn., assignorto American Cyanamid Company, Stamford, Conn. Continuation-impart ofabandoned application Ser. No. 118,748, Feb. 25, 1971. This applicationAug. 14, 1972,

Ser. No. 280,695

Int. Cl. C04b 35/00, 35/46 US. Cl. 106-42 2 Claims ABSTRACT OF THEDISCLOSURE Single crystal rutile boules modified with both tungsten andnickel are produced which vary in color from yellow to reddish amber.The boules are produced by mixing equimolar quantities of nickel andtungsten oxides .006- 0.3% NiO and 0.020.8% W by weight of TiO withrutile feed powder and fusing said mixture with a plasma or flame heatsource to form a single crystal boule. The boules produced havepotential utility as a gem material or in microwave maser applications.

The present invention relates to rutile single crystal boules. Morespecifically it relates to colored rutile single crystal boules and tothe production of such boules. This is a continuation-in-partapplication of US. patent application Ser. No. 118,748, filed Feb. 25,1971, now abandoned.

BACKGROUND OF THE INVENTION Rutile is one of the three known crystalmodifications of titanium dioxide. When substantially pure, a massivesingle crystal of rutile has gem-like properties; with a very lightstraw color; and, reflectance, refraction and brilliance greater thanthat of diamond.

Single crystals of rutile modified or doped with transition metal ionscould also be useful in semi-conductor applications. For example, one ofthe best materials for microwave masers in rutile doped with nickel. (L.C. Morris and D. J. Miller IEEE J. Quantum Electronics QE-l, 164, 1965.)

The preparation of colored rutile crystal boules whereby a yellow to redcoloration is caused by addition of either nickel oxide or cobalt oxideis described in US. Pat. No. 2,715,071 or blue coloration by theaddition of tungsten oxide and mixtures thereof is described in US. Pat.2,801,182. However, these boules are usually significantly moredifiicult to grow than pure rutile due to the difficulty ofincorporating the metal oxide into the rutile crystal lattice.

Although it is possible to incorporate various metal ions into a rutilecrystal by the high temperature diffusion method, rather than adding themetal ions during growth, the former process involves an extra diffusionstep which often requires more than 100 hours. Also, the maximumconcentration of metal ion or ions added to the rutile by diffusion isless than that which can be incorporated during growth.

Rutile mixed with small quantities of two metal oxides is a commercialyellow pigment. An example of such a pigment is rutile mixed with oxidesof nickel and antimony which is marketed by the Glidden Durkee Div. ofS.C.M. Corporation.

OBJECTS 7 OF THE INVENTION The principal object of the present inventionis the preparation of rutile single crystal boules, having colorsranging from yellow to amber, which may be used as gem material. Afurther object of this invention is the preparation of rutile singlecrystal boules modified with tungsten and nickel oxides. A furtherobject is to produce rutile boules so modified with oxides of tungstenand nickel WhlCh may be used as a quantum electronic material.

SUMMARY OF THE INVENTION In its broadest aspects the present inventioncontemplates a rutile single crystal boule containing as a coloringagent the combined oxides of tungsten and nickel in substantiallyequimolar amounts. These colored boules are prepared according to themethod of the present invention by progressively fusing a mixture offinely divided titanium dioxide and a small amount of said coloringagent mentioned above in a plasma or flame carrying an excess of anoxidizing gas to form said boule and thereafter oxidizing the boule soformed.

In this description of the present invention the word boule is used inits currently accepted meaning to denote a characteristic shape or formof an artificially prepared massive single crystal having a rounded end,or meniscus, a more or less rod-like body portion and a tapering end.

It has been found that rutile boules modified by additions of equal mole\quantities of tungsten and nickel are easier to grow than a boule grownusing a feed powder which contained a similar amount of nickel oxide,but with no tungsten oxide. The reason for the greater ease in growingrutile crystals when both nickel and tungsten are present, is postulatedto be due to charge balance which is possible in the lattice when metalions of both higher and lower valences than titanium are present. Bymeans of the present invention rutile single crystals may be produced invarious colors. Further, these large single rutile crystals modifiedwith more than one metal oxide additive can be used for making opticalmeasurements to evaluate various mixed oxide systems as candidates forcommercial colored inorganic pigments.

Many different oxides have been separately incorporated into a rutilehost crystal such as Ga O C00, NiO, A1 0 which are described in US.Pats. 2,756,157, 2,715,071, 2,715,070 and Gd O Eu O Sm- O and Cr O whichare reported elsewhere. In all cases the melting points of these oxideshave been higher than 1820 C., the melting point of the rutile host.However, in the present invention where a rutile crystal has beenmodified with oxides of both tungsten and nickel, the tungsten oxide, W0with a melting point of only 1473 C. was still retained in the boule.This was surprising, since it is normal during growth of crystalscomprising several components by the Verneuil technique, for the mostvolatile components to distill off from the molten cap of the bouleduring the crystallization process. The reason for the surprisingretention of W0 in the boule and thus the stability of this mixed oxidesystem is thought to result from the charge balance concept.

BRIEF DESCRIPTION OF THE DRAWING The drawing shows a comparison of theabsorption coefficients for rutile and rutile modified in accordancewith the invention. This modified rutile boule consists of 0.067 Weightpercent of MO, 0.208 weight percent of WC, and balance is T102.

DESCRIPTION OF THE INVENTION for preparing a feed material especiallyadapted for the production of rutile single crystal boules is described.

The small amount of the coloring agent, i.e., the oxides of tungsten andnickel, may be mixed with the TiO starting material in any convenientmanner, for instance, by

In progressively fusing the starting mixture of Ti and oxides of nickeland tungsten, there is employed a heat source which preferably containsoxygen. The heat source can be a plasma, preferred herein, or a flame.The fusion is carried out at a temperature of from 1825 C. to 1900 yblehdh'lg- A Particularly suitable feed material is one 5 C. Thetemperatureof the gas enveloping the boule should Where high P y z ismixed With reagent be carefully controlled during formation of theboule. grade thhgstic acid 4) and reagent g d nickel Rutile melts atabout 1820 C. and therefore it is necesllitl'ate hexahydfate s)2 2 insuch Proportions sary to operate so that the temperature at the top ofthe that the atomic ratios of TizWzNi are pre ent as 10 boule issomewhat above the melting point, e.g., 1825 C. 1'5:0.l:0.1. The mixtureis then calcined above 700 C. If the temperature is in excess of 1900"C. an excessively and ground in a mortar to obtain a feed material ofsuitlarge portion of the boule melts at the top and the molten ableconsistency. Alternatively, the oxides may be made by material runs overthe sides of the boule. For a plasma, Preparing the Phate double saltand argon or a similar inert gas is used as the carrier gas. Insubsequently calcining this. order for the plasma to be suitablyoxidizing it should con- The amount if coloring agent to be added to theTiO; min more than 2% oxygen.

feed material is' determined bythe color desired or more Excess oxygenin the boule enveloping gas is necessary precisely the location of theabsorption edge within the because at elevated temperatures, titaniumdioxide gives visible spectrum. For pleasing colors and good quality upoxygen and is converted to lower, or sub-oxides of tiboules the tungstenof the feed should not exceed 1% or 0 tanium, e.g., Ti O about 0.3% fornickel calculated as the element based on Even when operating with anexcess of oxygen, the the weight of the TiO;;. The amounts of coloringagent boule as produced has generally a deep blue-black color will varyto produce the various depths of colors and the indicative of somedeficiency in oxygen. Therefore, in orrange for each element will besubsequently described. der to produce a boule according to the instantinvention The preferred lower limit of the feed is about 0.005% for inwhich the color ranges from yellow through reddish nickel and 0.0017%for tungsten at which the boules proamber, the blue-black boule has tobe re-oxidized.

duced possesses a light yellow color. Concentrations of The reoxidationof the boule is preferably carried out by coloring agents below theabove lower limits result in heating the blue-black boule in anoxidizing atmosphere, boules substantially similar in color to plainrutile boules. for instance, air or oxygen. The temperature of thetreat- The single crystal rultile boules thereby produced have mentshould be within the range from about 650 C. to pleasing colors varyingfrom yellow to reddish amber. about 1500 C. It has been found that attemperatures to This is achieved by the presence of substantially equiyeXteHt below OXYgeH Will not he appreciably molar amounts of nickeloxide and tungsten oxide with the incorporated into the rutile Single yThere is a nickel oxide ranging from 0.006 to 0.3 weight percent cidedloss in brilliance, lustre and fire when the treatment based on thetotal weight of the boule. This range in turn s Carried out b ve 1 andat that temperature the defines the range of tungsten id hi h i from0.02 t rate of oxygen incorporated into the rutile crystal is ex- 0.8weight percent. A preferred concentration of i k l cessively rapid anddifiicult to control. Preferably the oxioxide ranges from 0,06 t6 ()7weight percent which in dation should be carried out at about 1100 C. to14-75 turn establishes that the equimolar range of tungsten ox- P p yanneal the boule- The heating should be ide is 0.19 to 0.23 weightpercent for this provides a transchhhhhed until the boule Obtains thedesired o parent, uniquely amber rutile crystal. at least hours at 1450Another requirement of the amounts of coloring agents, Accorfhhg to thePrhsent invention it is necessary to i.e., nickel oxide and tungstenoxide, is that they be pres- X oxldlze the hhle'hlack single 'y bouleWhen ent in substantially equal mole quantities in the feed mah thecolonhg agent in Order to revehl the charterial in order for them to bepresent in the boule in this actehshc h 9 of Such agent when the bouleis only ratio. The following model is suggested to explain the in-Parhahy oxldlzeq the true @0101 is masked by the blue of creasedstability of the solid solution system consisting of the,Xygeh h hohlethus Producing Colors having rutile modified with nickel and tungsten.bluish or green sh tone. The elements when added to It is known thatmetal ions incorporated into a rutile 5O T10 feed material produceboules having various colors. crystal lattice are usually insubstitutional sites. That is, The color of the homes vanes depth andtone When they occupy the position normally occupied by titanium theelements are present in diflierent amounts. When any i n+4) In prior artwhen a single metal oxide is of these elements are present in the boulein very small added to a rutile boule, ch.rlrge balance will not Occurquantities the color of the boule is yellow, varying from a withoutdefects or dislocations because the single cations paleyellqw to aYellow W1th a hrWhish t When P ha,e valghces other than For example, ifcharge bah ent in slightly larger quantities the rutile single crystalance was to obtain with two +2 valence metal ions then boule posseshhshh amber color when hreseht ih Shh either these two ions would both haveto occupy a Single larger quantities the color changes from a reddishamber titanium'ion substitutional site, or a defect or dislocation toahhhst i colormust occur in the lattice. Of these two possibilities, the"i lhustrahohof the quahty of h obhhhed from former is-unlikely sincethe relevant metal ion additives vanohs composlhohs of h Powder 1s gwehTable are quite Similar in Size to titanium According to this Theimproved boule quality resulting from the addition vgmjoh, however,since two metal ions are added to the of both tungsten and nickelcompared to that of nickel rutile lattice, one f which has a valencehigher than alone is shown, as is also the effect of concentration of +4he, w+6 and the other hi has a valence lower the tungsten and nickeladditives on boule color. than Ti, i.e., Ni+ then charge compensationcan occur In order to more fully illustrate this invention the when twotitanium ions are replaced by one tungsten and method of preparing theboule f the invention is hereone nickel ion. after described in theexample.

TABLE 1 Amount addition agent (calculated as atomic Addition agent i ilv thi e g ion m Condition of boule 5,3152%" furnace Nickel oxiderthstilt hiphmstahh sfhfiihltrltafisstiths.

Nickel oxide and tungsten oxide 0.1: D Ti:W:Ni=l5:0.5:

Good quality do Amber (tnansparent).

EXAMPLE To prepare the feed material for' atomic ratios ofTi:W:Ni=l5:0.1:0.1, 8.56 grams of 99.95+% TiO ('Gallard Schlesinger Co.)were mixed with 0.18 gram reagent grade H WO and 0.21 gram of reagentgrade Ni(NO '6H O. This mixture was slurried in water before grinding inan electric mortar. Then the mixture was calcined for 4 hours in afurnace at 1000 C. After grinding again in the mortar the powder wasscreened and that which passed through a No. 70 mesh screen was used asthe feed powder.

The feed powder, having an average particle size of 0.3 4 and composedof mainly TiO along with smaller quantities of W0 and NiO, was fed at aconstant rate of 0.05 gram/minute; suspended in an argon flow of 1liter/ minute; and passed by means of a cooled-probe through aninduction plasma. The plasma gas was a mixture of 97% argon and 3%oxygen; and, was admitted at the rate of 18 l./m. to a plasma torchconsisting primarily of a 28 mm. I.D. quartz tube in which power isinductively coupled to the gas, thereby cold gas and feed materialentered at the back and the hot gases and feed material were expelled atthe front into a 2 in. I.D., zirconia mufile. Positioned in the mufliejust below the torch and enveloped by the tail fi'ame from the plasma,the boule was located on the top of an alumina rod which was rotated andwithdrawn at the boule growth rate. A sight port in the muffle allowedconstant observation of the boule growth and measurement of temperatureby an optical pyrometer. A in. long boule, of diameter which varied fromV8 in. at the bottom to /2 in. at the top, was grown over a period of 4hours. The as-grown boule was black in color. After growing the boule itwas oxidized for 65 hours at 1425 C. in a tube furnace. The oxidizedboule was a yellow-amber color. A 1 millimeter thick slab, cut from theboule and polished, was transparent and consisted of 0.067 weightpercent of NiO, 0.208 weight percent of W0 and balance of TiO In orderto show the effect of the addition of nickel and tungsten oxide torutile, the measured absorption coeflicient of the boule of the exampleis plotted in the drawing for the visible region of the spectrum andcompared with a pure rutile crystal. The absorption edge is seen to beshifted about 500 A. to longer wavelengths and toward the red end of thevisible spectrum, and a residual absorption about 100 times greater thanthat of rutile was imparted to the boule by the nickel and tungstenoxides.

From the above description it has been shown that pleasant appearingcolored rutile boules may be formed by the present invention. Thecoloring agents produce products which range in color from yellowthrough amber to reddish-black tones when added in varying quantities.The precise depth of tone and nature of the color obtained is readilycontrolled as hereinbefore described by employment of the appropriatemixture. These colored boules may be cut into gems which possess therequired characteristics, particularly that of hardness and a pleasingappearance, which are necessary for the gem trade. They may also haveapplication as a quantum electronic material, for example, a microwavemaser.

While this invention has been described and illustrated by the exampleshown, it is not intended to be strictly limited thereto and othermodifications and variations maiy lie employed within the scope of thefollowing claims.

c aim: 1. A colored rutile single crystal boule containing oxides oftungsten and nickel in substantially equimolar amounts wherein said W0content ranges from 0.02 to 0.8 percent and said NiO content ranges from0.006 to 0.3 percent by weight based on said boule.

2. The boule of claim 1 wherein said W0 content ranges from 0.19 to 0.23percent and said NiO content ranges from 0.06 to 0.07 percent.

References Cited UNITED STATES PATENTS 2,715,071 8/ 1955 -Merker 106422,801,182 7/1957 Merker 10642 2,715,070 8/1955 Moore 10642 3,558,3331/1971 Beals 10642 FOREIGN PATENTS 686,490 1/ 1953 Great Britain 10642OTHER REFERENCES Johnson, G., et al.: Influence of Minor Additions onColor and Electrical Properties of Rutile, J. Am. Cer Soc. 32 (1949),pp. 398-401.

HEL'EN M. MCCARTHY, Primary Examiner US. Cl. X.R. 2330l UNITED STATESPATENT OFFICE A CERTIFICATE OF CORRECTION Patent No. 3796"58)+ DatedMarch 20, 197" Inventor(s) CHASE, JOHN DONALD It is certified that errorappears in the above-identified patent and that said'Letters Patent arehereby corrected as shown below:

Column 1, line 39, after the word masers, change "in" to is Column 3,line 16, after the word amount, change "ii" to of Signed and sealed this23rd day of July 1971 (SEAL) Attest:

c. MARSHALL DANN MCCOY GIBSON JR Commissioner of Patents AttestingOfficer P F RM P040550 (10-69) uscoMM-Dc 60376-P69 1 9 US. GOVIRNMINTPRINTING OFFICE z I!" 0-366-334

